1. Field of the Invention
The present invention relates generally to a high-rate packet data telecommunication system using multi-level demodulation, and in particular, to a method and apparatus for deshuffling shuffled data to the original data.
2. Description of the Related Art
A typical mobile communication system provides integrated support for voice service, circuit data, and low-rate (e.g., 14.4 kbps or lower) packet data. As user demand for high-rate packet data transmission such as Internet browsing and moving pictures has increased, the mobile communication system has been developed to support the high-rate packet data service.
Code Division Multiple Access2000 (CDMA2000), Universal Mobile Telecommunication Service (UMTS), and Wideband-CDMA (W-CDMA), which were proposed for the high-rate packet data service, adopt multi-level modulation in order to increase spectral efficiency. Multi-level modulation schemes include 8-ary Phase Shift Keying (8-PSK), 16-ary Quadrature Amplitude Modulation (16-QAM), and 64-ary QAM (64-QAM) which have higher modulation levels than Quadrature Phase Shift Keying (QPSK). These multi-level modulation schemes transmit a lot of information in each modulation symbol. They enable the high-rate packet data service, but require increased stable circuit quality.
In multi-level modulation, bits in one modulation symbol have different reliabilities. The different reliabilities lead to different average Bit Error Rates (BERs) at different bit positions. Codeword sequences output from a channel encoder having a plurality of constituent encoders such as a turbo encoder are divided into systematic symbols with a relatively high priority and parity symbols with a relatively low priority. Therefore, the systematic symbols are arranged at bit positions having a relatively high reliability and the parity symbols at bit positions having a relatively low priority in a modulation symbol, to thereby reduce the error rate of an information sequence in a receiver.
If a transmitter rearranges code sequences as described above, the receiver must recover the original information sequences. Since a system that processes a large volume of packet data at high rates usually has a data path for each data process unit, it needs a buffer for each data process unit.
As the number of buffers for data paths is increased in the receiver, time spent processing whole data is increased significantly. Moreover, when the transmitter shuffles code symbols prior to transmission, an additional buffer for deshuffling is required between demodulators for the data receiving paths and a decoder. As a result, data processing is delayed. Hence, there is a need for a method of efficiently using a deshuffling buffer and shortening a process time in deshuffling received shuffled data in a mobile communication system supporting high-rate packet data service.